This invention relates to a fuel injection pump for internal combustion engines, and more particularly to a starting injection timing advance device provided in such pump.
Internal combustion engines, particularly in double cell type Diesel engines, are difficult to start in cold weather. Conventionally, to facilitate starting of an engine of this type in cold weather, a glow plug is used to heat the suction air being supplied to the engine, and in some engines, a starting injection timing advance device is used to advance the fuel injection timing at the start of the engine, which device also serves to prevent occurrence of HC in the exhaust gases of the engine.
One of such starting injection timing advance devices has been proposed by Japanese Utility Model Provisional Publication No. 55-49078, which comprises an auxiliary piston arranged for urging contact with one end of a timer piston which forms part of an injection timing control device and is displaceable in response to fuel pressure variable as a function of the rotational speed of the engine, and having a larger pressure applying surface area than the timer piston, and a spring urging the auxiliary piston toward the timer piston. At the start of the engine, low fuel pressure acts upon the auxiliary piston so that the auxiliary piston is urged by the force of the spring to bias the timer piston in the injection timing advancing direction. As the engine speed subsequently increases, correspondingly increased fuel pressure causes the auxiliary piston to be displaced away from the timer piston against the force of the spring to then allow the latter to carry out a usual injection timing controlling action.
However, the proposed starting injection timing advance device is large in size because of its auxiliary piston having a large pressure applying surface area, and is therefore is difficult to install into a narrow mounting space in a vehicle or the like. Further, it is rather complicate in construction and not easy to assemble.